Semiconductor device having a frontside contact and vertical trench isolation and method of fabricating same

Abstract

There is a method of forming a contact post and surrounding isolation trench in a semiconductor-on-insulator (SOI) substrate. The method comprises etching a contact hole and surrounding isolation trench from an active layer of the substrate to the insulating layer, masking the trench and further etching the contact hole to the base substrate layer, filling the trench and contact hole with undoped intrinsic polysilicon and then performing a doping process in respect of the polysilicon material filling the contact hole so as to form in situ a highly doped contact post, while the material filling the isolation trench remains non-conductive. The isolation trench and contact post are formed substantially simultaneously so as to avoid undue interference with the device fabrication process.

1. A method of forming a contact post and a respective isolation trench in respect of an active semiconductor device region of a semiconductor-on-insulator substrate, said substrate comprising a base semiconductor substrate layer, a layer of insulating material on said base semiconductor substrate layer over which layer of insulating material is provided an active semiconductor layer within which an active semiconductor device can be formed, the method comprising
 forming a contact hole and surrounding trench, said contact hole extending from a surface of said active semiconductor layer to said base semiconductor substrate layer and said surrounding trench extending from a surface of said active semiconductor layer to said layer of insulating material, 
 providing the sidewalls of said trench with a dielectric layer, 
 completely filling said surrounding trench with a dielectric or substantially non-conductive semiconductor material and 
 partially filling said contact hole with a dielectric or substantially non-conductive semiconductor material and filling said contact hole the rest of the way with a substantially conductive semiconductor so as to form a conductive contact post. 
 
     
     
       2. A method according to  claim 1 , wherein said contact hole and surrounding trench are first filled with a substantially non-conductive semiconductor material, following which a diffusion process is performed in respect of said semiconductor material filling said contact hole only so as to introduce dopants into said semiconductor material and form the conductive contact post. 
     
     
       3. A method according to  claim 2 , wherein the dopant source for said diffusion process includes the dopants in said active semiconductor layer or a doped semiconductor material filled into said contact hole. 
     
     
       4. A method according to  claim 1 , the step of forming the contact hole and surrounding trench includes the sub-steps of
 etching a hole and surrounding trench which extend from the surface of the active semiconductor layer to the layer of insulating material, 
 filling said insulating trench with a dielectric material, and then further etching the hole to the substrate layer so as to form the contact hole. 
 
     
     
       5. A method according to  claim 1 , wherein the step of forming the contact hole and surrounding trench includes the sub-steps of substantially simultaneously etching a hole and surrounding trench which extend from a surface of the active semiconductor layer to the layer of insulating material,
 masking or otherwise protecting the trench and 
 then further etching the hole to the substrate layer so as to form the contact hole. 
 
     
     
       6. A method according to  claim 5 , wherein a dielectric layer is preferably deposited substantially simultaneously on the sidewalls of the trench and the hole, prior to the masking step, wherein subsequent etching of the hole to the substrate layer results in removal of the dielectric layer from the sidewalls thereof. 
     
     
       7. An integrated circuit die comprising a semiconductor-on-insulator substrate said substrate comprising
 a base semiconductor substrate layer 
 a layer of insulating material on said base semiconductor substrate layer, over which layer of insulating material is provided an active semiconductor layer within which an active semiconductor can be formed, said integrated circuit die includes a contact post and a respective surrounding insulation trench according to the method of  claim 1 . 
 
     
     
       8. A method of fabricating an integrated circuit comprising an active semiconductor device, the method comprising providing a semiconductor-on-insulation forming a respective contact post and isolation trench according to the method of  claim 1 . 
     
     
       9. An integrated circuit fabricated in accordance with the method of  claim 6 .